Keying circuit arrangement for transmitters



Aug. 30, 1932. w, BUSCHBECK 1,874,891

KEYING CIRCUIT ARRANGEMENT FOR TRANSNITTERS Fi led Aug. 24. 1929 AAAAAA VVIVI. L

INVENTOR B WERNER BUSCHBECK ATTORNEY Patented Aug. 30, 1932 UNITED STATES PATE CE;

WERNER BUSCHBECK, OF BERLIN, GERMANY, ASSIGNOR 'ro EEEETINK N i SCHAF'I' FUR DRAHTLOSE' TELEGRAPHIE'M. B. 11, or EEREINJGERMANX, ,AeooRPe I, RATION or GER-MANY I KEYING CIRCUIT ARRANGEMENT EoR "rRANsMIrTE s I Application filed August 24, 1929, Serial Nd. 388,108, and "i Germany June [30, 192 s.

Application for this invention was filed in scheme'shown in the prior. art the key Il is {I Germany, June 30,1928. A inserted between the grid 3 and the plate 4 This invention relates to transmitters and in particular to a novel keying means for 5 transmitters of thermionic type.

i i In transmitters of average and larger power, the energy to be handled by the keying relay is so large that operation with standard telegraph relays is no longer possible.

Since for reasons of high working speed and of cost it is not desirable to use large relays and large strokes, the keying arrangement heretofore used in connection with transmitter tubes is of a kind in which the tubes were connected for grid modulation. The grid of these tubes was rendered so markedly negative by means of a potential applied through a high resistance that the tube would be blocked. The key was disposed between the grid and the filament of the modulator tube.

In these schemes, the relay, in the first place, had the full grid direct current potential to ground (crest value of grid alternating current potential of the pilot tube, or even more when a biasing potential was employed). In the second place, the internal resistance of the modulator tubes, when grid and filament are united, is rather high, so that, to insure the desired direct current grid resistance, it was mostly necessary to provide a larger number of paralleled tubes.

The primary object of, this invention is to provide a novel keying system which will overcome the above defects.

85 Numerous other objects and advantages of my novel arrangement will be had from the specification and therefrom when read in connection with the attached drawing in which Figures 1 and 2 each show different modifi- 40 cations of the novel keying system as applied to a transmitter.

The circuit arrangement herein disclosed involves a transmitter relay tube H which has a high frequency input circuit 1 on which oscillations to be modulated are impressed.

Keying or modulating of the high frequency oscillations is accomplished through a keying tube M in the direct current input circuit of H as shown. The arrangement of the present invention difiers from the of the modulator or keying tube Mas shown rather than between the grid and the fila- I .ment of the said tube. The key-T may be either direct between the plate tand grid 30f M or else through a resistancelt as shown. When key T is in opened position, the keying tube Mis'blocked. .VVhen Tfis closed, the grid 3 of. M assumes a positive biasing potential with relation to its filament '5." The value of said biasing potentiahis governed by the value of the resistance. R, connectedin, series-with the key. In some casesithje grid 3 may have a. maximum value r 5 equalling that of the plate potentiah Under this condition, the tubena-turally has a far lower internal resistance, and as a consequencaa smaller number of keying tubes M Will su fiice." .Anotheradvantage 7 of the present arrangement is that the keying relay is grounded as shown. :This feature is desirable in case" of re-adjustment of the circuit elements ,during operation. Even in caseof a direct short-circuit of grid 7 3 and plate 4 of -M, only a small portion of the entire grid direct current necessary to key, H will flow by way 3 ofthekey'T'J In this manner large powers can be handled with a small sized keyingrel'ay. The oscilso lations modulated as set forth above appear onthe output electrodes 7 and 8 of H and may be utilized in any known manner.

The same keying circuit is suitable also for indicating modulated continuous wave trans- 8'5 mission. This is accomplished by the use of an oscillating modulator or'keying tube M of Figure 2. Here, as in the'prior figure, the grid direct current resistance R of the oscillating modulator or keying tube is con- '90 nected at the plate 4 of the modulator tube instead of at the filament according to former practice. In practice the said resistance R must be chosen so high that the grid di- I rect current flowing through it willcompensate the plate potential. Oscillation of tube M and the associated circuits is insured by the coupling between the tuned plate circuit 10 and the inductance 11 in the grid circuit when the key T is closed. Closing of the key T decreases the negative potential on the grid 3 of the tube M and renders said tube more conductive. This results in a large amount of rectified direct current flowing in the grid circuit of the tube H to pass between the cathode and plate of tube M. This direct current flowing in this circuit raises the positive potential on the plate. This positive potential is transmitted through the closed key T and resistance R to the grid of the tube M to overcome the negative potential applied thereto from the battery 16.

In both modifications biasing potential for the grid electrode 8 of tube M is supplied from a source 15 through a resistance 15. In both modifications the high frequency oscillations relayed in H are shunted around the keying circuits by a condenser C aInFigure 2 the keying oscillations produced in M are passed around the battery 16 and resistance 15 by a condenser G I I claim: 1. In a modulating means for an oscillation amplifier including, a thermionic tube having input and output elements, means for imodulating the oscillations repeated in said amplifier including, a thermionic keying tube having anode cathode and grid electrodes,

means for connecting the anode cathode imv pedance of said keying tube in parallel with the impedance between the input elements of said amplifier, an'impedance and a source of potential connected in parallel with the input impedance of said keying tube, and a keying circuit including, a fixed impedance and akey connected in parallel with the'impedance between the anode and grid electrode'of said keying tube.

2. An arrangement, as claimed in claim 1,

in which the circuit connected in parallel with the input elements of said keying tube includes an inductance and in which the keying circuit includes an inductance coupled to said first named inductance.

E NER BUSOHBEQK. 

